<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>FirstApp</title>
  <link rel="stylesheet" href="https://cdn.bootcss.com/twitter-bootstrap/3.3.7/css/bootstrap.min.css">
  <script src="https://unpkg.com/react@16/umd/react.development.js" crossorigin></script>
  <script src="https://unpkg.com/react-dom@16/umd/react-dom.development.js" crossorigin></script>
  <script src="https://unpkg.com/babel-standalone@6/babel.min.js"></script>
  <script src="https://unpkg.com/react-transition-group/dist/react-transition-group.js"></script>
  <style>
    .item-enter {
      opacity: 0;
    }
    .item-enter-active {
      opacity: 1;
      transition: opacity 500ms ease-in;
    }
    .item-exit {
      opacity: 1;
    }
    .item-exit-active {
      opacity: 0;
      transition: opacity 500ms ease-in;
    }
  </style>
</head>
<body>
  <div id="app"></div>
  <script type="text/babel" src="./app.js"></script>
</body>
</html>